1. Field of the Invention
The present invention relates to a feed mechanism to move a movable member using a sliding member which is supported by a hydrostatic bearing.
2. Discussion of the Prior Art:
In a machining apparatus for machining a workpiece into a non-circular shape, it is possible to use the feed mechanism, as shown in FIG. 5, for moving a tool. To be more specific, a cutting tool holder 3 with a cutting tool 2 is mounted on a front end of a square sliding shaft 1 through a piezoelectric actuator 4. The square sliding shaft 1 is held to be slidable in an axial direction by the force of oil which is fed to a hydrostatic bearing 6 formed between a guide base 5 and the square sliding shaft 1. In this arrangement, the square sliding shaft 1 is moved by a linear motor (not shown). With the synthesis of the driving motions by this linear motor and the piezoelectric actuator 4, the cutting tool 2 is moved in the direction perpendicularly crossing the rotational axis of the workpiece. The workpiece is thus machined in a non-circular shape.
Oil is fed to the hydrostatic bearing 6 as follows. First, oil stored in a tank 8 is pumped up with a hydraulic pressure pump 9, and pressurized oil discharged from the hydraulic pressure pump 9 lowers its pressure to a certain pressure level by means of a hydrostatic pressure reducing valve 10. The oil thus held at the reduced pressure is fed to the hydrostatic bearing 6 through an oil inlet channel 7 provided in the guide base 5. The oil thus fed into the hydrostatic bearing 6 is further led into an annular discharging channel 11 after being passed through the gap between the square sliding shaft 1 and the guide base 5. The oil is then fed back from the annular discharging channel 11 into the tank 8. In this regard, the reference numeral 8a represents an oil temperature controller, and the reference numeral 17 is a diaphragm which supports the cutting tool holder 3.
Moreover, the piezoelectric actuator 4, which is embedded in the front end of the square sliding 1, expands in accordance with the magnitude of the voltage applied to the actuator 4, thereby making the cutting tool holder 3 move minutely. Since the piezoelectric actuator 4 generates heat as the result of expansion movements, it is necessary to cool off the piezoelectric actuator 4. For the purpose of cooling this piezoelectric actuator 4, a cooling jacket 12 is provided, as shown in FIG. 5, at the outer circumferential area of the piezoelectric actuator 4. On its outer circumferential surface, the cooling jacket 12 is further provided with a helical oil channel 13 which communicates with the oil channels 3a and 13b formed within the square sliding shaft 1. Furthermore, a cooling oil feeding pipe 15a connects a hydraulic pressure pump 9 and a fixed connecting part 14. The connecting part 14 is communicated with the outer end of one oil channel 13a in the square sliding shaft 1 by means of a flexible hose 15. Likewise, the oil discharging pipe 16a, which connects the fixed connecting part 14 and the tank 8, is communicated with the outer end of the other oil channel 13b with a flexible hose 16.
In this case, elasticity of the hoses 15 and 16 cause resistance to the movement of the square sliding shaft 1, resulting in deterioration in the positioning accuracy of the square sliding shaft 1.
Moreover, the conventional structure had a problem that the piping system tends to be complicated, because many oil pipes are required to connect the cooling jacket 12 with the pump 9 and tank 8.